The Liquid Crystal Display (LCD) possesses advantages of thin body, power saving and no radiation to be widely used in many application scope, such as LCD TV, mobile phone, personal digital assistant (PDA), digital camera, notebook, laptop, and dominates the flat panel display field.
The Active Matrix Liquid Crystal Display (AMLCD) is the most common liquid crystal display device at present. The Active Matrix Liquid Crystal Display comprises a plurality of pixels, and each pixel is electrically coupled to a Thin Film Transistor (TFT). The gate (Gate) of the TFT is coupled to the horizontal scan line. The drain (Drain) of the TFT is coupled to the data line of the vertical direction. The source (Source) of the TFT is coupled to the pixel electrode. The enough voltage is applied to the level scan line, and all the TFTs electrically coupled to the horizontal scan line are activated. Thus, the signal voltage on the data line can be written into the pixel to control the transmittances of different liquid crystals to achieve the effect of controlling colors and brightness. The GOA (Gate Driver on Array) technology utilizes the array (Array) manufacture process of the thin film transistor liquid crystal display panel according to prior art to manufacture the driving circuit of gate row scan on the TFT array substrate for realizing the driving way of scanning the gates row by row. The GOA technology can reduce the bonding procedure of the external Integrated Circuit (IC) and has potential to raise the productivity and lower the production cost. Meanwhile, it can make the liquid crystal display panel more suitable to the narrow frame or non frame design of display products. Indium Gallium Zinc Oxide (IGZO) is an amorphous oxide containing Indium, Gallium and Zinc, and the carrier mobility is 20-30 times of the amorphous silicon thin film transistor, which is capable of magnificently raising the charging/discharging rate of TFT to the pixel electrodes to promote the response speed of the pixels and to realize faster refreshing rate. In the mean time, the line scan rate of the pixels also can be significantly promoted to make the production of the flat panel display with ultra high resolution possible. Besides the amount reduction of the transistors raise the transmission of each pixel. The IGZO display possesses higher efficiency level and the efficiency becomes higher.
With the development of the oxide semiconductor thin film transistor, such as IGZO, the peripheral circuit around the panel based on oxide semiconductor thin film transistor also becomes the focus that people pay lots of attentions. The oxide semiconductor thin film transistor has higher carrier mobility but the threshold voltage thereof is about 0V and the subthreshold range swing is smaller, the voltage Vgs between the gate and the source of many TFT elements as the GOA circuit is in off state generally is 0V. Thus, the design difficulty of the GOA circuit based on the oxide semiconductor thin film transistor will be increased. There will be some function issues happening when the design adaptable to the scan driving circuit for the amorphous silicon semiconductors is applied to the GOA circuit based on the oxide semiconductor thin film transistor. Besides, due to some external factor inductions and the stress effect, there will be a tendency that the threshold voltage diminishes toward minus value to the oxide semiconductor thin film transistor, which may directly result in malfunction of the GOA circuit for the oxide semiconductor thin film transistors. For example, at high temperature, the threshold voltage of the oxide semiconductor thin film transistor will move toward minus value to result in failure of the GOA circuit; similarly, under the function electrical stress function of light irradiation, the threshold voltage of the oxide semiconductor thin film transistor will move toward minus value. Therefore, the influence of the threshold voltage of TFT has to be considered as designing the GOA circuit based on oxide semiconductor thin film transistor.
As shown in FIG. 1, which is a GOA circuit based on oxide semiconductor thin film transistor which is available against the aforesaid issue, comprising a plurality of GOA unit circuits which are cascade connected, and the GOA unit circuit of every stage comprises a pull-up controlling module 100, a pull-up module 200, a transmission module 300, a first pull-down module 400, a bootstrap capacitor module 500 and a pull-down holding module 600. However, the GOA circuit based on oxide semiconductor thin film transistor remains a certain problem existing: the pull-down holding module 600 utilizes the signal of the first node Q(N) to control the ability of pull-down and deactivation. In condition that the element threshold voltage is forward biased, the ability of the pull-down holding module 600 being controlled by the voltage level of the first node Q(N) becomes weak and it cannot be normally deactivated. Accordingly, the first node Q(N) cannot be normally boosted up to the high voltage level in the functioning period, which results in the bad performance of the entire GOA circuit.